The present invention relates to an improved tube cutting apparatus and more particularly to a high-speed drum-type tube cutting machine designed for mass production cutting of tubes which could not be cut satisfactorily on conventional machines.
For many years mass production cutting of thin-walled tubes has been effected using semi-automatic drum-type cutting machines having rotating endless belts at the side of the drum adjacent the rotary cutters for engaging the tubes to hold them in parallel positions on the drum while rotating them at an angular velocity at least several times that of the drum and having a series of axially spaced rotary knives or cutters with cutting teeth located to project slightly beyond the internal surface of each tube. The endless belts cause each tube to rotate at least one revolution while in contact with the rotary cutters so that cutting is effected throughout the circumference of the tube.
These machines have performed extremely well and have been used extensively for almost two decades for gang cutting of tubes of small and medium diameter. However, prior to the present invention, certain gang cutting operations could not be performed satisfactorily on such machines. For example, gang cutting operations could not be performed satisfactorily when the tubes being cut had walls with insufficient thickness or insufficient strength or rigidly to maintain the circular cross section during cutting. If an attempt were made to cut large diameter tubes having readily deformable walls, these machines would not function satisfactorily because the cut pieces tend to collapse and be forced between the rotating cutters and the drum.
Gang cutting also presented serious problems if the tubes being cut had a very short axial length relative to the diameter because of the tendency of cut pieces to tilt and be chewed up by the rotary cutters. Gang cutting also was a problem when cutting tubes with walls of substantial thickness or substantial resistance to cutting by conventional rotary knives because the knives tended to bind and pull or force the tubes out of position during cutting. These various problems resulted in frequent malfunctions so that the automatic machines could not operate continuously in a reliable manner and were not considered satisfactory for commercial use.
Because of these problems, it was the practice prior to this invention to employ supporting mandrels when cutting thick tubes, large diameter tubes or tubes with flimsy or readily collapsible walls or when cutting washers or other pieces of very small axial dimension. This resulted in a great increase in the cost of the cutting operation and a reduction in the rate of production, particularly when the mandrels were loaded and unloaded manually.
Expensive automatic mandrel-type machines are available commercially which employ complicated reciprocating mechanisms to slide the tubes onto the mandrel and to remove the cut pieces, but the rate of production when using these machines is only a fraction of that which can be achieved on drum-type machines. Furthermore these mandrel-type machines require tubes with internal surfaces relatively free of dents, deformations or other internal defects which interfere with axial sliding of the tube over the mandrel. Malfunctions in these machines resulting from said internal defects or other problems can cause serious damage to the complicated mechanisms and present a serious safety hazard.
Another disadvantage of mandrels is that the rotating knives or cutters must be carefully positioned so that they do not cut the mandrel. Cleaner cuts are obtained when the knife or cutter projects beyond the internal surface of the tube being cut, less problems are encountered with the rotating cutter when cutting can be effected without mandrels.